(*
    In[1]:= func[20]
    Out[1]= {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
*)

Function[Typed[len, "MachineInteger"], Table[i, {i, len}]]